As much as I want to promote Linux, you do have to realize that there is going to be a learning curve. I use Linux exclusively, both on my desktops (at home, at work, and on my laptop) and on my servers (my job's a linux sysadmin). but I can't say you're going to be able to use it without issue and without a learning curve. It's a completely different OS, from the kernel level up through the userland tools.
Ubuntu's done a fantastic job of getting close, and you'll likely going to have minimal trouble using it for basic things, but there are still some steps you'll have to do manually. Small things like installing nvidia or ati restricted modules/drivers, which aren't really fault of Ubuntu as you have to do that on windows, but it will be a different process to doing it on Ubuntu/Linux than it would be in windows. Not necessarily harder, but different. You will likely have to install win32codecs and other packages to play mp3's and dvd's. Again, this isn't something that is a "problem" on Linux, because windows has this problem too (if you try installing windows xp from scratch, not from OEM packaged, it can't play MP3's or DVD's out of the box either), but since most OEM's bundle these codecs in with the system, most people don't notice it. There's even a possibility you could have to custom compile a kernel, edit an xorg.conf, or other such things that you've never done before.
You just have to realize that there IS a difference between Linux and Windows, and be ready to do a little bit of learning. There are great communities, and you will be able to get the answers you're looking for, but don't expect there to be no learning curve or problems.